Method of heating a hollow article

ABSTRACT

The invention relates to a method of deforming a portion of a hollow article with the aid of a plasma burner in such a manner that the section between the inner and outer walls is completely heated above its softening point.

Guyer...... l/1970 Rendina......... 3,321,662 5/1967 10 Claims, 3 Drawing Figures hollow article with the aid of a plasma bu manner that the section between the inner and outer walls is completely heated above its softening point.

Primary Examiner.l. V. Truhe Assistant Examiner-J. G. Smith AttorneyFrank R. Trifari ....no1j 1/90 [58] FieldofSearch.............................313/231,231X,240;

ARTICLE [72] lnventors: Raymond Francois Spiessens; Leiiert Schuringa; Ghislain Felix Alfons Arthur Verboven, all of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New York, NY.

[22] Filed: July 2, 1970 [21] App1.No.: 51,949

[30] Foreign Application Priority Data July 9, 1969 Netherlands.......................

[52] U.S. [51] Int.

United States Patent Spiessens et al.

54] METHOD OF HEATHNG A HOLLOW PATENTEDFEBZBIQYZ 3.846.308

' sum 1 OF 2 4 Fig.1 7

N TOR? PATENTEDFEBZQ I972 SHEET 2 BF 2 METHOD OF HEATING A HOLLOW ARTICLE The invention relates to a method of heating a hollow article of a material which is poorly electrically conducting at least at room temperature, the heat treatment taking place by means of 'an electric gas'discharge which is generated by an induction field'of highfrequency in the cavity of the article.

A method of the kind described in the preamble is described, for example, inNetherlands patent application Ser. No. 6,509,968. In this Netherlands patent application there is described how a closed layer of a protective material may be provided on the inner wall of a tube with the aid of an electric gas discharge in said tube. Said patent application states that it must be ensured that the wall of the tube does not become too wall thickness of the hollow body above its softening point with the aid of a plasma burner so as'to be able to bring about a deformation.

' Although it is known to heat an article with the aid of gas flames and to deform it subsequently, this has the drawback I that very local heat treatments are difficult to carry out and that the method furthermore involves all kinds of contaminations. In addition this method requires a comparatively long heating period.

According to the invention a method of heating a hollow article of a material which is poorly electrically conducting at least at room temperature, in which the heat treatment takes place by means of an electric gas discharge which is generated by an induction field of high frequency in the cavity of the article is characterized in that the product of intensity and duration of the field is so great that a wall section of the article extending from the inside to the outside is completely heated up to above the softening point of said wall section, whereafter a deformation takes place.

An advantage of this solution is that a wall section from the cavity, hence from the interior, can be heated very locally and comparatively quickly in order to deform it, for example, in order to be able to form a pinch of a lamp. Particularly such a heat treatment from the cavity creates more possibilities for the design of, for example, the pinch. A further advantage is that no contaminations of gases occur in this method. In a device according to the invention the wall of the plasma 1 burner is in fact also the wall of the article to be worked.

through one aperture of the article and may be conducted away through a different aperture to escape into the free atmosphere. A method according to the invention may likewise be performed in a room process in which gas in a flowing state is not used.

The material of the article may be, for example, quartz or glass or a ceramic material because a high temperature may be reached with the plasma.

A'method according to the invention may be used, for example, to seal a hole which is initially present in the wallof the hollow article by heating the materials provided around this hole and by causing them to flow together. It is alternatively possible that a further article is sealed in or on the hollow article.

In a special embodiment of a method according to the invention in which the hollow article is a component of a future lamp, the wall section is deformed with the aid of a pinching device and this in such a manner that a vacuumtight sealing of the cavity is obtained at the area of the deformation. This is a method which is particularly advantageous for the manufacture of lamps because the heat treatment does not involve substantially any contaminations.

It is possible that the deformation is only intended to seal a cavity. In a further advantageous method according to the invention a member provided with an electric supply conductor is inserted after the heat treatment into the cavity of the article at the height of the heated wall section, which wall section is subsequently pinched around this member in a vacuumtight manner.

Such an advantageous method may be used, for example, in the manufacture of incandescent lamps. The member provided with an electric conductor is then formed, for example, by the filament including the electric supply conductors. It is feasible. that the gas atmosphere is present in and around the entire article. In that case the cavity will, however, be bound to a minimum size because otherwise no discharge occurs in the cavity but only occurs outside this cavity.

In a further advantageous method according to the invention in which the hollow article is a component of a, future lamp and in which an exhaust tube is provided on said component, the gas for the electric gas discharge for heating the wall section is supplied through the exhaust tube and is conducted away from the article through a different aperture.

A very simple supply and exhaust of the gas is possible in case of this solution.

In an advantageous method according to the invention the gas for the electric discharge for the heat treatment of the wall section is supplied through a hollow needle of a satisfactorily thermally conducting material, which needle is passed through the exhaust tube and in which at least one gas exhaust aperture is provided near the tip of the needle.

An advantage of the last-mentioned solution is that the needle also ensures that no discharge occurs in the gas supply duct. Such a discharge might lead to unwanted heating.

For igniting the discharge, for example, an article provided in the cavity may first be brought to a high temperature so that a number of atoms of the gas is ionized, whereafter the field of high frequency can ignite the gas and maintain the discharge.

In a special method according to the invention the electric discharge for heating the wall section is ignited with the aid of an auxiliary device of high frequency an electrode of said auxiliary device of high frequency being placed near an aperture of the article and the discharge being maintained by the induction field of high frequency after the discharge has been ignited.

An advantage of this method is that a reliable ignition of the discharge may be obtained.

The heat treatment and the deformation of the wall section may be performed on the same area in the apparatus.

In a special method according to the invention the article is moved, after heating the wall section, to an auxiliary device in which the deformation is performed.

An advantage of this preferred solution is that deformation is then not hampered by parts of the heating device of high frequency such as, for example, by a coil for generating the field of high frequency.

A device according to the invention preferably includes a movable holder (in which the article to be worked is placed) which holder is present in one position near the coil which is connected to the high-frequency generator and is present near a pinch block in a different position.

A simple movement of the article from the heating area to the deformation area is possible with the aid of such a holder.

In order that the invention may be readily carried into effect, a few embodiments thereof will now be described in detail, by way of example with reference to the accompanying diagrammatic drawings, in which FIG. 1 shows a device performing a method according to the invention and an article to be worked,

FIG. 2 shows a detail of the device of FIG. I at a following working stage,

FIG. 3 shows the same details as in FIG. 2, but at a later manufacturing stage.

In FIG. 1, the reference numeral 1 denotes an envelope including an exhaust tube of a future incandescent lamp. The envelope section is denoted by the reference numeral 2 and the exhaust tube section is denoted by 3. The material of this hollow article is quartz. The exhaust tube 3 of this lamp 1 is placed in a holder 4, which is connected to a conveyor mechanism 5. A hollow needle 6 is inserted into the exhaust tube 3, the tip of which needle is present just inside the envelope 2. This needle 6 is made of chromium nickel. This needle 6 is connected through a supply, duct 7 of synthetic plastics material to a reservoir 8 containing argon gas. The

reference numeral 9 denotes a regulating device. The 1 reference number 10 denotes a gas exhaust aperture in the tip of the needle 6. The reference numeral 11 denotes an ignition device which is connected through a wire 12 and a conveyor mechanism 13, to an ignition pin which is devoted by the reference numeral 14. The ignition device 11 is fed through two connecting terminals 15 and 16 of the device which is intended to be connected to an alternating voltage mains of, for example, 220 v., 50 Hz. The terminal 15 is connected through a switch 17 and a connecting wire 18 to the ignition device 11. The terminal 16 is connected through a wire 19, a tapping 20 and a wire 21 as well as a contact 22 to the ignition device 11. The reference numeral 23 denotes a high-frequency generator. This generator is likewise fed through the connecting terminals l and 16. A coil 25 which has two windings is connected through a time switch 24 to the generator 23. An energizing winding of a relay is connected in series with this coil 25 between the generator 23 and the coil 25. This energizing winding is denoted by the reference numeral 26. The work contact of this relay is denoted by the reference numeral 22. The reference numerals 27 and 28 denote pinch blocks. The reference numeral 30 denotes an auxiliary member for the future lamp 1. In FIG. 1, the auxiliary member 30 is shown twice. The member shown on the right-hand side is the one seen in the device according to the invention. The member shown on the left-hand side shows a situation as is seen when the member 30 is rotated 90 over its longitudinal axis. The second illustration of the member 30 in FIG. 1 is intended to clarify the structure of this member. The member 30 comprises a filament 31 and two molybdenum supply conductors, which are denoted by 32 and 33, respectively. The molybdenum supply conductor 32 is connected to a supply wire 34. A molybdenum conductor 33 is connected to a supply conductor 35. The supply conductors 34 and 35 are clamped in an auxiliary device which is denoted by the reference numeral 36. The reference numeral 37 denotes an exhaust aperture for an inactive gas which flows around the parts of the member 30 which gas prevents oxidation of these parts of the member 30. The gas is, for example, nitrogen. The future lamp 1 is shown (in broken lines) in a second position in the winding 25.

The method to be performed with this device is the following. First, argon gas from the reservoir 8 is supplied through the regulating mechanism 9 and through the duct 7 to the needle 6 in the exhaust tube 3. The gas evolves from a few apertures provided in the tip of the needle, flows through the interior of the hollow article 2 and is conducted away from the aperture thereabove. Subsequently the conveyor mechanism 5 is activated so that this mechanism 5 lifts the envelope 1 (with the needle 6) upwards by means of the holder 4 up to the position shown in a broken line. Subsequently the pin 14 is provided above the aperture of the lamp 1 with the aid of the conveyor 13. See the positions of 13 and 14 shown in broken lines. The switch 17 is then closed so that the device 11 is activated. As a result the pin 14 will inject free electrons into the evolving argon gas. Subsequently a discharge in the argon gas is ignited at the area of the winding 25. The high-frequency generator 23 which is also activated by changing over the switch 17 will take over the maintenance of this discharge once a discharge is present in the argon gas. In fact, when as a result of a discharge sufficient current will flow through the winding 25 and hence through the winding 26, the contact 22 will be opened. Consequently, the auxiliary device 11 is switched off. As soon as the current starts to flow through the winding 25, the time switch 24 is automatically switched on. This time switch is set, for example, at 5 seconds. When these 5 seconds have elapsed, the time switch automatically switches off the generator 23,so that no further discharge is maintained in the argon gas. The duration and intensity of the discharge-in the argon gas in the winding 25 is such that the upper wall of the cylinder of the part 1 becomes incandescent.

Subsequently the conveyor mechanism 5 returns the envelope l to the position shown by solid lines. The device 36 and the member 30 will thereafter be lowered, namely through the winding 25 until the position shown in FIG. 2 is obtained (the pin 14, see FIG. 1, is timely put into the position shown by the solid lines). The reference numerals in FIG. 2 correspond to those in FIG. 1. In FIG. 2 the situation is shown in which part of the member 30 is present in the upper aperture of the envelope 1. In this situation the upper part of the cylinder 2 is still incandescent.

Subsequently the two pinch blocks 27 and 28 are moved towards each other so that a flat pinch is formed. This situation is shown in FIG. 3. Also in this FIG. 3, the same reference numerals have been used for the same components as those in the previous Figures. Due to the two pinch blocks 27 and 28 approaching each other the hot, weak parts of the cylinder 2 are clamped around the member 30. After this has been pinched for some time the two pinch blocks 27 and 28 are :moved away from each other and a waiting period of a few instants is observed until the envelope 1 has cooled down. The device 36 is then lifted upwards, but now without the member 30. Subsequently, the envelope is removed from the holder 4 :and the exhaust tube is connected elsewhere to a fitting filler gas reservoir and is then sealed in some manner. It is feasible that this exhaust tube is sealed in a corresponding manner with a plasma burner as described with reference to the device shown.

It is possible that a different gas instead of argon gas is used, or that optionally a different gas is supplied after ignition. It is likewise possible that the process described is carried out in a closed room where there is no question of a flowing gas but a stationary gas. This may be, for example, again argon or, for example, nitrogen or a different gas.

The process described related to an incandescent lamp. However, such a process may be used alternatively for providing a pinch or for providing an electrode in a discharge lamp. As compared with the previously common methods in which gas flames were used, the method described is very simple. Particularly the supply of a well-defined quantity of energy, for example, by means of a time switch 24 as shown in FIG. I, is a great advantage of such a device.

It is of course possible that the device includes more than one coil connected to a high-frequency generator and that two or more future envelopes to be heated in the various coils are simultaneously lifted upwards in a holder.

What is claimed is:

l. A method of deforming a wall of a hollow article comprising introducing an ionizable medium into said hollow article, applying a high-frequency induction field to the hollow part of the article to generate an electric gas discharge in said ionizalble medium to heat said article to a temperature at which a portion of the wall from the inner to the outer surface thereof softens, and maintaining said hollow article in said field until a deformation of said wall portion can be realized, the product of the intensity of said field and the duration thereof being such that said wall portion is completely heated up to and above the softening point of said wall section.

2. A method as claimed in claim 1 further comprising pinching said wall portion to obtain a vacuumtight closure of the hollow part of the article.

3. A method as claimed in claim 1 further comprising inserting a member provided with a current conductor into the hollow part of the article and pinching said wall portion to obtain a vacuumtight closure of the hollow part of the article.

4. A method as claimed in claim I wherein introducing an ionizable medium into said hollow article comprises supplying gas through an exhaust tube and conducting said gas away through a different aperture.

5. A method as claimed in claim 4 wherein supplying gas through an exhaust tube comprises using a hollow needle of a satisfactory thermally conducting material, and conducting said gas away comprises using at least one gas exhaust aperture provided near the tip of said hollow needle.

6. A method as claimed in claim 1 wherein applying an induction field of high frequency in the hollow part of the article to generate an electric gas discharge in said ionizable medium to heat said article comprises igniting said discharge by placing an electrode of an auxiliary device of high frequency near an aperture of said article and subsequently maintaining said discharge by the high-frequency induction field.

7. A method as claimed in claim 1 further comprising moving said article to an auxiliary device to perform deformation,

8. A method as claimed in claim 1 further comprising switching off the high-frequenty induction field when said product of intensity and duration of said field have been reached.

9. Apparatus for deforming a wall of a hollow article comprising means for introducing an ionizable medium into said hollow article, means for applying a high-frequency induction field within the hollow part of the article to generate an electric gas discharge within said ionizable medium to heat said article to a temperature at which a portion of the wall between the inner and the outer surfaces soften, means for maintaining said hollow article in said field until the product of the intensity of said field and the duration is such that said wall portion is completely heated up to and above the softening point of said wall section, and means for pinch sealing the wall portion of said hollow article thereby deforming said wall portion.

10. Apparatus for deforming a wall of a hollow article as claimed in claim 9 further comprising a moveable holder for said hollow article, said holder having a first position near said high frequency induction field means and a second position near said pinch sealing means. 

1. A method of deforming a wall of a hollow article comprising introducing an ionizable medium into said hollow article, applying a high-frequency induction field to the hollow part of the article to generate an electric gas discharge in said ionizable medium to heat said article to a temperature at which a portion of the wall from the inner to the outer surface thereof softens, and maintaining said hollow article in said field until a deformation of said wall portion can be realized, the product of the intensity of said field and the duration thereof being such that said wall portion is completely heated up to and above the softening point of said wall section.
 2. A method as claimed in claim 1 further comprising pinching said wall portion to obtain a vacuumtight closure of the hollow part of the article.
 3. A method as claimed in claim 1 further comprising inserting a member provided with a current conductor into the hollow part of the article and pinching said wall portion to obtain a vacuumtight closure of the hollow part of the article.
 4. A method as claimed in claim 1 wherein introducing an ionizable medium into said hollow article comprises supplying gas through an exhaust tube and conducting said gas away through a different aperture.
 5. A method as claimed in claim 4 wherein supplying gas through an exhaust tube comprises using a hollow needle of a satisfactory thermally conducting material, and conducting said gas away comprises using at least one gas exhaust aperture provided near the tip of said hollow needle.
 6. A method as claimed in claim 1 wherein applying an induction field of high frequency in the hollow part of the article to generate an electric gas discharge in said ionizable medium to heat said article comprises igniting said discharge by placing an electrode of an auxiliary device of high frequency near an aperture of said article and subsequently maintaining said discharge by the high-frequency induction field.
 7. A method as claimed in claim 1 further comprising moving said article to an auxiliary device to perform deformation.
 8. A method as claimed in claim 1 further comprising switching off the high-frequenty induction field when said product of intensity and duration of said field have been reached.
 9. Apparatus for deforming a wall of a hollow article comprising means for introducing an ionizable medium into said hollow article, means for applying a high-frequency induction field within the hollow part of the article to generate an electric gas discharge within said ionizable medium to heat said article to a temperature at which a portion of the wall between the inner and the outer surfaces soften, means for maintaining said hollow article in said field until the product of the intensity of said field and the duration is such that said wall portion is completely heated up to and above the softening point of said wall section, and means for pinch sealing the wall portion of said hollow article thereby deforming said wall portion.
 10. Apparatus for deforming a wall of a hollow article as claimed in claim 9 further comprising a moveable holder for said hollow article, said holder having a first position near said high frequency induction field means and a second position near said pinch sealing means. 